Schrödinger's cat is a thought experiment, usually described as a paradox, devised by Austrian physicist Erwin Schrödinger in 1935. It illustrates what he saw as the problem of the Copenhagen interpretation of quantum mechanics applied to everyday objects. The thought experiment presents a cat that might be alive or dead, depending on an earlier random event. In the course of developing this experiment, he coined the term Verschränkung (entanglement).[1]

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This artwork by F. Gwynplaine MacIntyre, originally published in Analog magazine, illustrates MacIntyre's science-fiction story "Schrödinger's Cat-Sitter". The cat occupies a quantum superposition relative to the tined object, being simultaneously in front of and behind the object, which itself occupies a quantum superposition because it is simultaneously a square-edged object with two tines and a round-edged object with three tines.

It was not long before science-fiction writers picked up this evocative concept, often using it in a humorous vein.[2] Several have taken the thought experiment a step further, pointing out extra complications which might arise should the experiment actually be performed. For example, in his novel American Gods,Neil Gaiman has a character observe, "if they don't ever open the box to feed it, it'll eventually just be two different kinds of dead." Likewise, Terry Pratchett's Lords and Ladies adds the issue of a third possible state, in the case of Greebo, "Bloody Furious". (In Pratchett's later novel The Last Hero, Death attempts the experiment himself, but cannot understand the mechanics of it, wondering if it implies that he will kill the cat just by looking at it.) In Will Grayson, Will Grayson, by John Green and David Levithan, the Cat makes an appearance as an analogy for Will and Jane's relationship.

Douglas Adams describes an attempt to enact the experiment in Dirk Gently's Holistic Detective Agency. By using clairvoyance to see inside the box, it was found that the cat was neither alive nor dead, but missing, and Dirk's services were employed in order to recover it, Dirk deducing that the cat had simply grown tired of being subjected to the experiment and wandered off (Although he admits later on that he was actually using the experiment as an attempt to determine the mental state of his friend Richard Macduff, Richard's logical arguments about why the experiment was pointless confirming that he was mentally stable).

In Libba Bray's book Going Bovine, three stoners argue whether the cat is alive or dead, or whether the person who opens the box creates the possibilities. There are constant references to a band called Copenhagen Interpretation, who disappear into thin air in the middle of a benefit concert.

In "Schrödinger's Cat-Sitter" by F. Gwynplaine MacIntyre (published in Analog magazine, July/August 2001), a time-traveler named Smedley Faversham visits the past to interview Erwin Schrödinger but gets tricked into taking care of Schrödinger's wife's cat while she is away and Schrödinger is visiting Max Planck. In attempting to take care of the cat, Faversham inadvertently locks it in a cabinet with a Geiger counter, a vial of acid, and a hammer, unintentionally enacting Schrödinger's thought experiment, but with results that remain as uncertain as in the original case.

The title character (though not a main character) of Robert A. Heinlein's "The Cat Who Walks Through Walls", a kitten named Pixel is of indeterminate existence, and as such, has the ability to turn up in places that are specifically sealed to outside access. When this ability is questioned, the answer is "He's Schrödinger's cat", leading to the response, "Then Schrödinger had better come get him."

In Glynne MacLean's 2009 short story Viennese Meow Schrödinger's cat tells his version of the famous thought experiment.[3]

In the Hellsing manga series by Kouta Hirano, one of the depicted Nazis is an artificial catboy named Schrödinger. He claims that he is everywhere and nowhere at the same time, which is similar to the cat being alive and dead at the same time.[4] It is also said that he can only exist as long as he is aware of himself. In the second anime adaption, he eventually allows himself to be absorbed by the vampire Alucard, which causes his awareness to be clouded. This then spreads to Alucard, who vanishes for thirty years.

On a somewhat more serious level, Ian Stewart's novel Flatterland, (a sequel to Flatland) attempts to explain many concepts in modern mathematics and physics through the device of having a young female Flatlander explore other parts of the "Mathiverse". Schrödinger's Cat is just one of the many strange Mathiverse denizens she and her guide meet; the cat is still uncertain whether it is alive or dead, long after it left the box. Her guide, the Space Hopper, reassures the Cat with a modern view of quantum decoherence. Ursula K. Le Guin wrote a story entitled "Schrödinger's Cat" in 1974 (reprinted in The Compass Rose, published in 1982), which also deals with decoherence. Greg Egan's novel Quarantine, billed as "a story of quantum catastrophe", features an alternative solution to the paradox: in Egan's version of quantum mechanics, the wave function does not collapse naturally. Only certain living things—human beings among them—collapse the wave function of things they observe. Humans are therefore highly dangerous to other lifeforms which require the full diversity of uncollapsed wavefunctions to survive.

In the 2003 novel, Vernon God Little by DBC Pierre, the concept is discussed by the Vernon and Jesus characters. It is erroneously attributed by Jesus to the German philosopher Immanuel Kant.

Also, in the young adult novel Will Grayson, Will Grayson, by authors John Green and David Levithan, one of the main characters is perplexed by the concept of Schrödinger's Cat, and references it throughout the book.

In the play Schrodinger's Girlfriend, the future Nobel Prize winner finds himself falling under the spell of cabaret singer and seductress Hansi Haas, who has already had her way with Einstein, Planck and Bohr. As he wrestles with his love and the problems of wave theory, Hass throws him over for Paul Dirac, revealing a truth that holds for both love and quantum physics: "if you never ask the question, the answer can still be yes." (Review of play at Playbill[5]Critical review of play at SFGate[5])

In MacSchrödinger's Cat a 2010 novel by James Conor O'Brien set in a multi-verse romp across the universes centring around Venice in search of a missing scientific experiment concerning a trans-dimensional cat, Janis Joplin as God, and a panoply of caricatures of physics and physicists ranging from James Clerk Maxwell, Erwin Schrödinger to String Theory, the Big Bang and infinitely annoyed monkeys.

Fiction writers have confined other animals besides cats in such contraptions. Dan Simmons's novel Endymion begins with hero Raul Endymion sentenced to death by imprisonment in a "Schrödinger box".

Kōsuke Fujishima's manga series Ah! My Goddess featured a play on Schrödinger's Cat. During one storyline, a storage room was expanded to infinite proportions and the main characters encountered a Schrödinger's Whale, an extremely rare species with the ability to travel through space-time in a five-dimensional quantum state. The male lead in the series, Keiichi Morisato, befriends the whale and teaches it songs by real-life musical group The Carpenters (in the original English translation, it was Matthew Sweet) - but their time spent together is short, for the whale must move on or risk its safety as its wave function collapses. Because of this need to keep moving through quantum states, Schrödinger's Whales hardly ever meet, the reason they are so thin on the ground — but miraculously, Keiichi secured the future of the species by teaching it the songs. After discovering the whale had gone, he found out that it had learned Only Yesterday by itself (Missing Time in the translation) - this gave the whales a call that they could locate each other by.

In Peter Milligan's metaphysical comic Animal Man, Schrödinger's Cat is explained using a theory of pizza delivery mix-ups, resulting in both pepperoni and plain pizzas occupying the unopened box.

In the Stargate SG-1 episode, "Enigma" (1998), Samantha Carter gives a pet cat named Schrödinger to Narim. After explaining the name Schrödinger, Narim comments that his society calls that concept Kulivrian physics. Narim's response to Carter's inquiry about whether or not he has studied it is: "Yes, I've studied it...among other misconceptions of elementary science."[6]

In the Futurama episode, "Mars University" (1999), Professor Farnsworth is lecturing on the effects of quantum neutrino fields and the blackboard behind him displays an explanation of "Superdupersymmetric String Theory" and a diagram explaining "Witten's Dog". Witten's Dog, named after Ed Witten, is a parody of the classic Schrödinger's cat paradox. Astrophysicist David Schiminovich created both the equations and the diagram, based on "an equation that constrains the mass density of neutrinos in the universe".[7] Also the episode, "Law and Oracle" (2011), features an extended car chase scene in which Police Officer Fry apprehends Erwin Schrödinger, who is transporting a box containing "a cat, some poison and a cesium atom." When asked if the cat is alive or dead, Schrödinger responds that "it is a superposition of both states, until you open it and collapse the wave-function." Upon opening the box, Fry finds a living cat, who attacks him, while his partner discovers "there's also a lot of drugs in there." It is later revealed that the cat has agreed to testify against Schrödinger.

In the Doctor Who audio adventure Zagreus, the Eighth Doctor is transformed into the destructive Zagreus after he is exposed to an anti-time explosion after he was forced to use his TARDIS to contain it- anti-time being as destructive to time as anti-matter is to matter-, but shifts between his own personality and the 'Zagreus' personality, realising that as long as he remains in the TARDIS, the universe cannot decide which personality is in control, noting the similarities between this situation and the Schrödinger's Cat experiment.

In the Numb3rs episode "Identity Crisis" (2005), Charlie Eppes and Larry Fleinhardt discuss the Schrödinger's cat paradox in relation to how can a man be both guilty and not guilty of a crime.

In the Yu-Gi-Oh! GX episode, "It's All Relative" (2006 Japan, 2007 USA), Dr. Eisenstein uses a card known as "Schrödinger's Cat", which allows him when he draws outside his Draw Phase to shuffle the drawn cards back into his deck and draw the same number of cards again.

In The Big Bang Theory episode, "The Tangerine Factor" (May 19, 2008), Leonard's attempt to arrange a date with Penny results in both Penny and Leonard's seeking Sheldon's advice. Sheldon advises Penny that "just like Schrödinger's cat being alive and dead at the same time", her date with Leonard currently has both "good and bad" probabilistic outcomes. The only way to find out is to "open the box", in other words collapse the wave-function of an uncertain date into a specific outcome. Also, in the episode "The Russian Rocket Reaction" (October 13, 2011), Sheldon characterizes his relationship to Leonard as "Schrödinger's friendship", in the sense that Leonard is simultaneously his friend and mortal enemy (as he may or may not attend Wil Wheaton's party). When Sheldon tries to explain the paradox to Penny, she gives an approximate description: "...] there's this cat in a box and until you open it, it's either dead or alive or both [...]". Penny references it during a brief conversation with her new boyfriend in "The Codpiece Topology" (September 29, 2008), and Leonard references it during lunch with the guys in "The Bus Pants Utilization" (January 6, 2011).

In Season 1, episode 6 of FlashForward, "Scary Monsters and Super Creeps" (2009), Simon references Schrödinger's Cat as he is trying to explain why the blackouts happened. He describes it using the metaphor of holding a tiny cat in a closed hand with a poisoned sardine. If the cat eats the sardine, he will die; if not, he will live. But the outcome will be unknown until the hand is opened. Until then, the cat may be both alive and dead simultaneously, with reality ultimately being decided upon the intrusion of an observer.

Charlie Brooker, on his program Newswipe (2009), refers to the media coverage of Jade Goody's death as paradoxical in the same way that Schrödinger's cat is. He shows a visual metaphor using a stuffed cat to explain, then comments,"But that's the Copenhagen Interpretation of quantum mechanics for you."

Nearly a third of an episode of the series, Sayonara, Zetsubou-Sensei is devoted to Schrödinger's cat, referencing it in the way that there are infinite possibilities for anything in a box. Examples include Schrödinger's lunch box (which may or may not have mold), Schrödinger's boxed-wives (which could all possibly be ideal), and refusing to face reality (by boxing things with possibly bad outcomes).

In Space Dandy's season 2 episode "I can't be the only one, Baby", which centers around string theory, one of the alternate dimension versions of main character Meow is a Schrödingarian, an alien race composed by literal Schrödinger's cats.[8]

In A Serious Man (2009), written by the Coen Brothers, protagonist Larry Gopnik mentions Schrödinger's Cat in a discussion about the unpredictability of future events.

In Repo Men (2010), Jude Law's character mentions the Schrödinger's cat example in the beginning of the movie.

In 6 Films to Keep You Awake: The Baby's Room (2006), a Spanish made-for-TV movie, a journalist, Domingo, describes Schrödinger's Cat to the protagonist, Juan, in order to explain the existence of parallel worlds.

In The Prestige (2006), Nikola Tesla uses a cat to demonstrate a machine he makes for The Great Danton.

In Prince of Darkness (1987), Walter and Catherine have a discussion about Schrödinger's Cat, with Catherine understanding and Walter not.

In the short film "Dead and Alive" (2013) by Desert Eagle Pictures, the situation of the main character Cynthia runs parallel in many ways to that of the Schrödinger's Cat thought experiment. The distinction is most evident in the classroom scene, where a high school physics teacher gives a lecture on the aforementioned feline.[9]]

In the low-budget science fiction movie Coherence (2013), Schrödinger's Cat is the principle driving the alternative universes that occur during the movie.

In Digital Devil Saga, a game produced by Atlus, there is an enigmatic cat-like creature revealed to have some connection to God, whom the main character can see throughout the games. His name is 'Schrödinger'.

In Wild Arms 3, the character of Shady the Cat, owned by a Maya Schrödinger, is based on Schrödinger's cat, and is claustrophobic as a result of the "experiment."

In NetHack, one of the monsters encountered in this roguelike game is called 'Quantum Mechanic', which often carries a chest. The chest either contains a cat corpse, or causes a cat to appear. Reading the source code to the game also reveals that the game does not determine the state of the cat until the chest is opened.

In Pop'n Music, a song titled Schrödinger's Cat was composed by Tomosuke Funaki for the arcade version of Pop'n Music 16 PARTY. It is credited as the first song in the series with a 43 difficulty rating, the highest difficulty level in the series.

In Portal, GLaDOS tried to replicate the experiment with the scientists from Aperture Science, and she settled that the cat was dead. In the ending of its sequel, Portal 2, the Fact Sphere might say "The Schrödinger's cat paradox outlines a situation in which a cat in a box must be considered, for all intents and purposes, simultaneously alive and dead. Schrödinger created this paradox as a justification for killing cats." In the publicity web-comic for the game, the fate of the protagonist Chell is a reference to Schrödinger's Cat. GLaDOS also mentions a "bring your cat to work day" and that she has the boxes and the neurotoxins (poison) and just needs the cats. There is also an achievement called Schrödinger's Catch, awarded when the player catches a blue box before it touches the ground, after it is broken out of a glass receptacle.

In Gundeadligne, the first stage is "Le chat noir de Schrödinger - Schrödinger's Black Cat", This stage's boss is called "Chatnoir", whose appearance is that of a Cat girl (nekomimi).[10]

In Elements the Game, Schrödinger's Cat is an Entropy creature that has an ability Dead and Alive. This activates death effects without killing the cat.

In the visual novelUmineko no Naku Koro ni, episode 3, the main character Battler uses Schrödinger's Cat in his battle against the witch Beatrice to deny the existence of magic. The remainder of the visual novel continuously refers to this as "cat box".

In BlazBlue: Continuum Shift, after a fight between Tager and Lambda-11, during Tager's storyline, Kokonoe references Lambda-11 and Tager being similar to two Schrödinger's Cats. Also Terumi is both dead and alive, and can only exist as long as he is being observed, but in this case being observed might be an emotional response to his actions.

In Bioshock 2, hidden within a mass of ice, there is a deceased cat. Upon melting the ice and closely examining it, the display reads "Schrödinger".

In Zero Escape: Virtue's Last Reward, there is a book named Schrödinger's Cat in one room, and the thought experiment is eventually used in two parts of the game's plot; the identity of the masked person known as K is different in different endings, and whether or not the old woman is dead or alive also depends on the ending.

In Borderlands 2, Patricia Tannis makes mention of Schrödinger's "zombie cat" being to blame when describing the possibility that digistructed loot chests might contain either great loot or "nothing but crappy white shields".

In Ghost Trick: Phantom Detective, we have two examples: Yomiel, the original bad guy, who was a man that was neither alive nor dead, as his body constantly regenerated because of the power of a meteorite that entered his back and lodged in his heart; and Sissel which becomes a more literal example after going 10 years in the past to save his master Yomiel from such fate, but in turn the meteorite lodged inside the black cat himself, allowing him to be both dead and alive.

In PuzzleCraft, when farming, a treasure chest will occasionally contain one cat. The first time this happens the player unlocks the "Schrödinger's Cat" achievement.

MS Paint Adventures, in an extra from the Problem Sleuth adventure, the Midnight Crew used Schrödinger's cat to deal with a meddlesome wasp.[23] The fate of Nepeta Leijon of Homestuck also references Schrödinger's cat.

In The Noob Comic, Schrödinger's cat is featured on a blackboard in a lecture about how to exploit Clichequest's (the game the comic takes place in) bugs using string theory; the drawing of the box with the cat in it accompanied by the question "If dead, does it drop any loot?".[24]

Eyedea: On the "Infrared Roses" track from his 2001 CD, The Many Faces of Oliver Hart, Eyedea proclaims, "The curiosity that killed Schrödinger's cat was the only thing that kept it alive, matter of fact".

Mark Rosengarten: On his 2007 CD, Schrodinger's Cat Strikes Back, this high-school chemistry teacher [26] performs a song that humorously depicts Schrödinger's Cat getting her revenge for such a diabolical idea.

The Ghost of a Saber Tooth Tiger: Sean Lennon (son of John) and Charlotte Kemp Muhl released a song entitled "Schroedinger's Cat" on their 2010 album "Acoustic Sessions." The lyrics apply principles from quantum mechanics to relationships with the line, "Can't be sure that I exist when you are not around."

The song Love and Hatred by The Crüxshadows features the lyrics, "Can you hear the cat within the box, can you hear electrons moving free, watching something, watching nothing, in status somewhere in between..."

The ecommerce website ThinkGeek sells a t-shirt based on the Schrödinger's cat experiment.[27] One side of the shirt reads, "Schrödinger's cat is dead." The other side reads, "Schrödinger's cat is not dead." This parodies the concept of the cat being both dead and alive. The site also sells a shirt for women which reads "Hello Schroddy", and features a white box with a red bow, being a play on both Schrödinger's Cat and Hello Kitty.[28] The description reads, "This might not be Hello Kitty. It might be Goodbye Kitty. We cannot possibly know without observing, and then we change the outcome." ThinkGeek also sells a box with a sliding door, which activates an internal electronic display to show an animation of either a living or deceased cat.[29] The box has a sign reading "WARNING: MAY OR MAY NOT CONTAIN LIVE ANIMAL".

The website Shirt.woot! offers four shirts based on the cat. First, a psychedelic t-shirt based on the cat;[30] second, a t-shirt featuring the formula as a calligram in the shape of a cat;[31] third, The Cat in the Box by Dr. Schrödinger, a parody of Dr. Seuss' Cat in the Hat.;[32] fourth, a Venn diagram, with the cat in the intersection between alive and dead.[33]

The website TeeTurtle sells a shirt with a glow-in-the-dark design that has a cat and reads "Schrödinger's Cat Is ALIVE" when bright; the eyes cross out and reverts to read "Schrödinger's Cat Is DEAD" in the dark.[35]

Huffposthill reported, "Between 1999 and 2002, Mitt Romney was somehow in charge of Bain and not in charge of Bain, making him the Schrodinger's cat of corporate executives", referring to the discrepancy between what Romney said about his involvement in Bain Capital after 1999 and what was actually reported by Bain Capital documentation.[36]

^[* In the short film "Dead and Alive" (2013) by Desert Eagle Pictures, the situation of the main character Cynthia runs parallel in many ways to that of the Schrödinger's Cat thought experiment. The distinction is most evident in the classroom scene, where a high school physics teacher gives a lecture on the aforementioned feline. "Dead and Alive"].